Implantable defibrillator apparatus

ABSTRACT

An implantable defibrillator apparatus having a plurality of defibrillation electrodes which can be applied to the heart muscle in order to apply electric defibrillation shocks thereto, and defibrillation-control means for selectively applying respective electric defibrillation shocks to the electrodes preferably sequentially in time and in synchronism with the QRS.

[0001] This is a continuation of application Ser. No. 09/299,699, filedApr. 26, 1999, the contents of which are hereby incorporated herein byreference.

FIELD OF THE INVENTION

[0002] The present invention relates to defibrillation techniques, andin particular relates to atrial defibrillation.

BACKGROUND OF THE INVENTION

[0003] Atrial fibrillation (often referred to simply as AF), in itschronic and paroxysmal forms, constitutes the arrhythmia that is mostfrequent in the population, with a particularly high incidence (10%) inadults aged over 65 years. There is no pharmacological treatment whichis sure to be effective and, as for all antiarrhythmic drugs, there isan increased probability of inducing serious ventricular proarrhythmia.In patients who are suffering from this condition to an incapacitatingextent and who do not respond to the use of an average of two to threeantiarrhythmia drugs, the subject of an alternative solution becomesimportant.

[0004] An implantable atrial defibrillator with an associatedventricular stimulation/sensing capability constitutes a recenttreatment which is currently at the clinical evaluation stage. Adefibrillator of this type is usually implanted by the insertion in theheart of two electrodes (leads) having large active surface areas andconstituted by metal coils which are positioned along the outer wall ofthe right atrium and in the coronary sinus, whilst the metal containerof the defibrillator can also operate as an active pole duringdischarge.

[0005] The basic object of defibrillation is to produce an electricfield adequate to involve, anatomically, a significant portion of themyocardium of both atria, in order to depolarize, by means of theelectric shock, a predominant number of myocardial cells which aresubject to spontaneous, chaotic and non-synchronized electricalactivity. Recent tests have shown the great importance of thedistribution of the electric field in minimizing defibrillation energyand consequently voltage, muscle-stimulation and perception of pain,which constitutes the most important factor limiting the use of thesedevices.

SUMMARY OF THE INVENTION

[0006] The object of the present invention is to provide a defibrillatorwhich can achieve an effective action antagonistic to fibrillation.

[0007] In one aspect, this invention is an implantable defibrillatorapparatus comprising a plurality of defibrillation electrodes adapted tobe applied to the heart muscle and to deliver electric defibrillationshocks thereto, the plurality of electrodes in communication withdefibrillation-control means capable of selectively supplying voltagepulses to the electrodes, wherein the defibrillation control meanscontrols the duration and interval of the voltage pulses and furtherwherein the voltage pulses produce electric defibrillation shockssufficient to produce defibrillation. Preferably, the electricdefibrillation shocks are sufficient to produce defibrillationsynchronized with the heart's QRS, and the control unit can deliverdefibrillation shocks to the electrodes in a desired time sequence. Thecontrol unit may selectively vary at least one characteristic of theelectric defibrillation shocks, including the waveform of thedefibrillation shock, the duration of the defibrillation shock, theinterval between successive defibrillation shocks, and the electrodes towhich a defibrillation shock is applied at any particular time. Theapparatus may also comprise sensor means for detecting the occurrence ofa fibrillation phenomenon, the sensor means being connected to thecontrol unit and adapted to activate the application of defibrillationshocks. The sensor means may comprise respective sensing lines thatconnect the plurality of electrodes to the control unit to enable theelectrodes to act both as defibrillation electrodes and as sensingelectrodes. The apparatus may also comprise sensor means capable ofdetecting a ventricular electrogram. The control unit may synchronizethe application of defibrillation shock during the QRS of theelectrogram.

[0008] In another aspect, this invention is an implantable defibrillatorapparatus comprising a plurality of defibrillation electrodes adapted tobe applied to the heart muscle and to deliver electric defibrillationshocks thereto; the plurality of electrodes in communication withelectronic switches; the electronic switches in communication with apower stage capable of supplying voltage pulses to the electrodes,wherein the power stage is connected to a control unit that controls theduration and interval of the voltage pulses and further wherein thevoltage pulses are applied for a time sufficient to producedefibrillation.

[0009] In yet another aspect, this invention is a method of treatingatrial fibrillation comprising providing a stimulating device having aplurality of electrodes; inserting the plurality of electrodes atdesired locations in the heart; and applying defibrillation shocks tothe plurality of electrodes in a desired sequence, thereby creating anelectric field having a geometry designed for the patient's anatomy.Sensing atrial fibrillation may be done by means of the plurality ofelectrodes or by means of a specialized sensor.

BRIEF DESCRIPTION OF THE DRAWING

[0010]FIG. 1 shows a block diagram of the circuit structure of amulti-pole defibrillator according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0011] Basically, the solution according to the invention enables theatrial defibrillation shock to be split up physically and over time soas to reduce the energy delivered.

[0012] In a preferred embodiment, the implantable atrial defibrillatorof this invention comprises at least two electrodes that can be insertedpermanently in the heart chambers. Each electrode has a surface arearanging from 50 to 100 mm². The electrodes permit the delivery ofelectric shocks in a programmable manner, sequentially in time, betweenany electrode or pole or group of electrodes or poles belonging to thesame or to different leads, in order to defibrillate the fibrillatingatria in an optimal manner.

[0013] The electrical characteristics of the shock and, in particular,the waveforms (single-phase, symmetric two-phase and asymmetrictwo-phase, etc.), the duration, and the interval between successiveshocks (on the order of about 100 microseconds) can be programmed.

[0014] When atrial fibrillation has been confirmed by sensing of thechaotic atrial activity detectable by one or more poles of the sameleads or by means of a specialized sensor, the sequence ofdefibrillation discharges is activated by sensing of the ventricularelectrogram, detected by a suitable lead located in the right ventricle.This activation takes place in synchronism with the so-called QRS of theelectrocardiograph signal to prevent dangerous proarrhythmia. Thesequence has a programmable duration, by way of indication, no longerthan 50 milliseconds, such that it is sure to be included within in theabsolute refractory period of the ventricular myocardium.

[0015] Since the functional relationship between impedance and surfacearea of a conductor pole immersed in blood is hyperbolic, for surfaceareas greater than about 50 to 100 mm², reduced variations occur inimpedance as a function of surface area. In the currently preferredsolution for implementing the invention, a low shock voltage thussuffices to produce, at each of the above-described poles, a currentdensity equal to that which requires voltages even three to four timesgreater in the single poles of large surface area which are usedpredominantly at the moment. It is consequently possible to achieveeffective atrial defibrillation with reduced perception of pain, whichis caused mainly by the voltage. The multi-pole configuration alsopermits the creation of an electric field of variable geometry designedfor the patient's anatomy, which can further reduce the need for highvoltages.

[0016] The invention will now be described with reference to FIG. 1,which shows a plurality of electrodes (or “poles”), indicated 1, 2, 3, .. . n, that can be fitted in sites of the heart suitable for bringingabout an effect antagonistic to fibrillation (defibrillation),particularly with regard to atrial fibrillation (AF), by the applicationof electric signals (shocks).

[0017] The structural characteristics of these electrodes, for example,the selection of constituent materials, any surface treatment, etc., arethose currently used in known implantable defibrillators.

[0018] In particular, the term “electrode” or “pole” as used herein isintended to define any electrically-conductive member which can beassociated with the heart muscle in a relationship suitable for thetransmission of an electrical signal. Consequently, the electrodes orpoles in question may either be configured as physically separatemembers which are thus intended to be fitted in distinct and separaterespective myocardial sites, or may be associated in groups or sets withrespective supporting structures (so-called “leads”) so as to be fittedin respective myocardial sites separately (in the sense that eachelectrode or pole can transfer—and detect—a respective signal to— andfrom—the myocardium) but not independently, since the electrodes orpoles of each group disposed on a respective lead are implantedsimultaneously as a result of the implantation of the respectivesupporting element.

[0019] The apparatus may comprise two electrodes, or in more complexconfigurations, the number n may equal, for example, ten electrodes.Preferred numbers of electrodes typically range from three to five.Electrodes 1 to n may either be identical to one another or may havedifferent shapes according to the sites in which they are to bepositioned.

[0020] In general, electrodes 1 to n preferably have a surface areatypically of the order of 50 mm² or more, for example, 100 mm². Since,as mentioned above, the functional relationship between impedance andsurface area of a conductor pole immersed in blood is typicallyhyperbolic, with surface-area values of the type indicated, a low shockvoltage (for example 50 to 100 volts) suffices to produce a currentdensity in each of the electrodes equal to that which required theapplication of voltages even three to four times greater in the (single)electrodes of known implantable defibrillators.

[0021] The apparatus comprises defibrillation control means having powerstage 4; electrodes 1, 2, 3, . . . to n; electronic enabling switches11, 12, 12, . . . , in; and timing and control unit 37, whose operationis described as follows.

[0022] Power stage (the “high voltage” stage) 4 of the implantabledefibrillator generates voltage pulses which are applied to electrodes1, 2, 3, . . . to n, via respective electronic enabling switches orcontrol gates 11, 12, 13, . . . , 1 n.

[0023] Switches or control gates 11 to 1 n are connected to respectiveenabling lines 21, 22, 23, . . . , 2 n, thus allowing the signalsgenerated in power stage 4 to pass selectively towards electrodes 1, 2,. . . n). Switches or control gates 11 to 1 n communicate with and arecontrolled by timing and control unit 37, preferably provided withtelemetering interface 37 a of generally known type.

[0024] The control performed by control unit 37 by means of lines 21,22, 23, . . . 2 n enables the characteristics of the defibrillationsignals applied to the myocardium to be programmed, in particular withregard to the following characteristics:

[0025] the waveform: single-phase, symmetric two-phase and asymmetrictwo-phase, etc.,

[0026] the duration of each shock,

[0027] the interval between successive shocks, and

[0028] the ability to activate the defibrillation pulses in the variouselectrodes 1, 2, 3, . . . , n sequentially in time (in accordance with atypical time-sharing scheme).

[0029] As a result, the above-described multi-pole configurationpermits, in particular, the creation of an electric defibrillation fieldof variable geometry designed for the patient's anatomy, by virtue ofthe ability to program the emission of the control signals by controlunit 37. This permits a further reduction in the intensity (in practice,the voltage) of the signals applied; this results in an ability toachieve effective atrial defibrillation with low pain perception sincethe latter is caused mainly by the voltage.

[0030] The defibrillation may be activated by sensing of the chaoticatrial activity in the presence of fibrillation, which may be detectedby means of specialized sensor 5 of generally known type. However, in aparticularly preferred embodiment of the invention, it is possible toreplace and/or to supplement this conventional sensing with sensingperformed by the electrodes 1, 2, 3, . . . n themselves. Respectivesensing lines, generally indicated 6, are provided for this purpose andenable the electrical signals indicative of the local myocardialactivity at the respective implant site to be detected by the respectiveelectrode so as to supply to control unit 37 a set of signals whichenables control unit 37 to see and to identify the occurrence of afibrillation phenomenon.

[0031] The block diagram of FIG. 1 shows multiplexer 7, that enables thesignal coming from one or more of electrodes 1, 2, 3, . . . n, to bedetected selectively by the respective sensing line 6. After anti-noisefiltering performed in filter 8 and automatic gain control performed inautomatic gain-control circuit (AGC) 9 controlled by control unit 37 bymeans of line 10, the sensing signals thus detected reach comparatorcircuit 30. Here, the sensing signals are compared with a thresholdlevel, which may be adaptively modifiable, and which is supplied bycontrol unit 37 by means of line 31.

[0032] Finally, a sensor (of known type), indicated 32, can detectventricular activity and can supply to the unit a correspondingsynchronization signal such that control unit 37 can synchronize theapplication of the shock sequence by the electrodes 1 to n with theventricular QRS.

[0033] Moreover, the various electronic components shown in the drawing(or at least those of low power) clearly may either be in the form ofdiscrete blocks or components, or may be integrated in a single circuit.

[0034] According to known criteria, the sensing operation is regulatedin a manner such as to prevent a sensing signal from being picked upfrom an electrode which is being used at the time in question for theapplication of a defibrillation signal. In particular, as alreadymentioned, the sequence of defibrillation discharges is activated bysensing of the ventricular electrogram detected by sensor 32, preferablylocated in the right ventricle, so as to have a programmable duration,by way of indication, no greater than 50 milliseconds, which is sure tobe included within the absolute refractory period of the ventricularmyocardium.

[0035] Naturally, the principle of the invention remaining the same, thedetails of construction and forms of embodiment may be varied widelywith respect to those described and illustrated, without therebydeparting from the scope of the present invention, as defined by thefollowing claims.

What is claimed is:
 1. An implantable defibrillator apparatuscomprising: a plurality of defibrillation electrodes adapted to beapplied to the heart muscle and to deliver electric defibrillationshocks thereto; the plurality of electrodes in communication withdefibrillation-control means capable of selectively supplying voltagepulses to the electrodes; and wherein the defibrillation control meanscontrols the duration and interval of the voltage pulses and furtherwherein the voltage pulses produce electric defibrillation shockssufficient to produce defibrillation.
 2. The implantable defibrillatorapparatus of claim 1 wherein the electric defibrillation shocks aresufficient to produce defibrillation synchronized with the heart's QRS.3. An apparatus according to claim 1 , wherein the control unit isadapted to deliver defibrillation shocks to the electrodes in a desiredtime sequence.
 4. An apparatus according to claim 1 , wherein thecontrol unit is adapted to selectively vary at least one characteristicof the electric defibrillation shocks, the at least one characteristicselected from the group of waveform of the defibrillation shock, theduration of the defibrillation shock, the interval between successivedefibrillation shocks, and the electrodes to which a defibrillationshock is applied at any particular time.
 5. An apparatus according toclaim 1 , wherein the apparatus further comprises sensor means fordetecting the occurrence of a fibrillation phenomenon, the sensor meansbeing connected to the control unit and adapted to activate theapplication of defibrillation shocks.
 6. An apparatus according to claim5 , wherein the sensor means comprise respective sensing lines thatconnect the plurality of electrodes to the control unit to enable theelectrodes to act both as defibrillation electrodes and as sensingelectrodes.
 7. An apparatus according to claim 1 , wherein the apparatusfurther comprises sensor means capable of detecting a ventricularelectrogram, and wherein the control unit synchronizes the applicationof defibrillation shock during the QRS of the electrogram.
 8. Animplantable defibrillator apparatus comprising: a plurality ofdefibrillation electrodes adapted to be applied to the heart muscle andto deliver electric defibrillation shocks thereto; the plurality ofelectrodes in communication with electronic switches; the electronicswitches in communication with a power stage capable of supplyingvoltage pulses to the electrodes; and wherein the power stage isconnected to a control unit that controls the duration and interval ofthe voltage pulses and further wherein the voltage pulses are appliedfor a time sufficient to produce defibrillation.
 9. An apparatusaccording to claim 8 , wherein the control unit is adapted to deliverdefibrillation shocks to the electrodes in a desired time sequence. 10.An apparatus according to claim 8 , wherein the control unit is adaptedto selective vary at least one characteristic of the electricdefibrillation shocks, the at least one characteristic selected from thegroup of waveform of the defibrillation shock, the duration of thedefibrillation shock, the interval between successive defibrillationshocks, and the electrodes to which a defibrillation shock is applied atany particular time.
 11. An apparatus according to claim 8 , wherein thesuccessive defibrillation shocks are applied at intervals ofapproximately 100 microseconds.
 12. An apparatus according to claim 8 ,wherein the electrodes have a surface area ranging from about 50 mm² toabout 100 mm².
 13. An apparatus according to claim 8 , wherein theapparatus further comprises a sensor for detecting the occurrence of afibrillation phenomenon, the sensor being connected to the control unitand adapted to activate the application of defibrillation shocks.
 14. Anapparatus according to claim 13 , wherein the sequence of defibrillationshocks has a duration no greater than approximately 50 milliseconds. 15.An apparatus according to claim 13 , wherein the sensor comprisesrespective sensing lines that connect the plurality of electrodes to thecontrol unit to enable the electrodes to act both as defibrillationelectrodes and as sensing electrodes.
 16. An apparatus according toclaim 8 , wherein the apparatus further comprises a sensor capable ofdetecting a ventricular electrogram, and wherein the control unitsynchronizes the application of defibrillation shock during the QRS ofthe electrogram.
 17. A method of treating atrial fibrillationcomprising: providing a stimulating device having a plurality ofelectrodes; inserting the plurality of electrodes at desired locationsin the heart; and applying defibrillation shocks to the plurality ofelectrodes in a desired sequence, thereby creating an electric fieldhaving a geometry designed for the patient's anatomy.
 18. The method ofclaim 17 further comprising the step of sensing atrial fibrillation bymeans of the plurality of electrodes.
 19. The method of claim 17 furthercomprising the step of sensing atrial fibrillation by means of aspecialized sensor.
 20. The method of claim 17 wherein the step ofapplying defibrillation shocks further comprises a control unit incommunication with plurality of electrodes, the control unit controllingthe characteristics of the defibrillation shocks by means of one of thewaveform, the duration, the interval between shocks, and the sequence ofactivating shocks to various electrodes.